Is the sore on the top or pad of the foot?
Do you know what caused the sore?
Hi Sammy, I am soon going off line so since you have not responded to my info request I am going to give you a few ideas.
If the wound is on the pad, they act like shock absorbers so each time the dog walks on it will spread open which will cause the area to open again. You can clean it with providone iodine, apply a triple antibiotic ointment on it, tape thick gauze with cotton in between the layers to further cushion the foot, then place a sock over that. Anytime you wrap a foot it should not be done too tightly or you will cut the circulation. You want to look at the wound every couple of days as well and re wrap.
If it is on top of the paw you can do the same, cleaning gauze and sock but you wont need the thickness of cotton in between.
If the dog can access the area then he may pull off any bandaging so it may be a good idea to got to the pet store and invest in an Elizabethan collar. This should prevent the dog from licking the area.
It is also possible that at this point the dog needs oral antibiotics as their mouths carry a lot of bacteria and licking can cause a huge infection so if you don't see any improvement after wrapping and applying an ointment then you will want to have your vet look at it.
It should heal but it will take longer if he is able to lick it. You may be able to make a collar at home depending on the size of the dog. I'll direct you to a site that can show you how to do this. Continue to clean the wound several times a day and continue to put a triple antibiotic ointment on it.
Elizabethan collars: home made
homemade bite not collars: